CN114543685B

CN114543685B - Interferometer modulator, measurement system and measurement method

Info

Publication number: CN114543685B
Application number: CN202011328905.3A
Authority: CN
Inventors: 陈鲁; 白园园; 马砚忠; 张嵩
Original assignee: Shenzhen Zhongke Feice Technology Co Ltd
Current assignee: Shenzhen Zhongke Feice Technology Co Ltd
Priority date: 2020-11-24
Filing date: 2020-11-24
Publication date: 2024-06-04
Anticipated expiration: 2040-11-24
Also published as: CN114543685A

Abstract

The application discloses an interferometer modulator, a measuring system and a measuring method. The system includes a light emitting assembly, an interferometric modulator, a time delay, and a detector. The light emitting assembly generates pump light and probe light. The interferometer modulator is arranged on a transmission light path of the pump light and is used for carrying out amplitude modulation on the pump light; the interferometric modulator includes an interferometric component and a phase difference adjustment component. The time delay device receives the pump light or the probe light, so that the delay time between the pump light pulse and the probe light pulse is adjustable. The detector acquires signal light formed by reflection of detection light by an object to be detected under a plurality of delay times, and acquires detection information according to the signal light. Since the cost of the interferometric modulator is much lower than that of the acousto-optic modulator and the electro-optic modulator, the use of the interferometric modulator to amplitude modulate the pump light in the measurement system can save costs. Meanwhile, compared with an acousto-optic modulator and an electro-optic modulator, the interferometer modulator has stronger stability and ensures higher light utilization rate.

Description

Interferometer modulator, measurement system and measurement method

Technical Field

The present application relates to the field of measurement technologies, and in particular, to an interferometric modulator, a measurement system, and a measurement method.

Background

The film thickness measurement by using optoacoustic is a precise optical measurement technology, the film thickness measurement range is 50A-10 um, and the precision can reach 0.1A. In this technique, an acousto-optic modulator or an electro-optic modulator or a chopper is typically applied to amplitude modulate the pump light. The optical energy utilization rate of the acousto-optic modulator is low, and the crystals of the electro-optic modulator have deliquescence risk in the air for a long time. The cost of the acousto-optic modulator, the electro-optic modulator and related supporting facilities can reach hundreds of thousands of yuan, and the cost is high. Therefore, how to realize light amplitude modulation at low cost at the time of photoacoustic measurement has become a technical problem that needs to be solved urgently in the art.

Disclosure of Invention

Based on the above-described problems, the present application provides an interferometric modulator, a measurement system, and a measurement method, which realize light amplitude modulation at low cost at the time of photoacoustic measurement.

The embodiment of the application discloses the following technical scheme:

In a first aspect, the present application provides an interferometric modulator comprising: an interference assembly and a phase difference adjustment assembly;

The interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the first pump light and the second pump light are pulse light;

The phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light.

Optionally, the phase difference adjusting component is specifically configured to make a time difference between two pump light pulses formed by splitting the same pump light pulse and returning to the interference component be zero or an integer multiple of a repetition time period of the pump light pulse.

In a second aspect, the present application provides a measurement system comprising: a light emitting assembly, an interferometric modulator, a time delay, and a detector;

the light emitting component is used for generating pump light and detection light, and the pump light is pulse light;

The interferometer modulator is arranged on the transmission optical path of the pump light and is used for carrying out amplitude modulation on the pump light; the interferometric modulator includes: an interference assembly and a phase difference adjustment assembly; the interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light;

The time delay device is used for receiving the pumping light or the detection light, so that the delay time between the pumping light pulse and the detection light pulse is adjustable; the detection light and the pump light emitted by the time delay device are incident to an object to be detected; or the pump light and the detection light emitted by the time delay device are incident to the object to be detected; the pump light is used for forming sound waves in the object to be detected;

the detector is used for acquiring signal light formed by reflecting the detection light by the object to be detected under a plurality of different delay times and acquiring detection information according to the signal light.

Optionally, the interference assembly includes: a first coupling assembly, a first mirror, and a second mirror;

The first coupling component is used for dividing the pump light into two beams;

The first reflecting mirror and the second reflecting mirror are respectively used for receiving a beam of pump light transmitted by the first coupling component and reflecting the received pump light back to the first coupling component; the pump light reflected from the first mirror and the pump light reflected from the second mirror interfere at the first coupling assembly;

the phase difference adjusting component is used for adjusting the phase difference of the two beams of pump light reflected back to the first coupling component;

Or the interference component comprises a light splitting component and a second coupling component, wherein the light splitting component is used for splitting pump light and generating the phase difference of the split pump light to form first pump light and second pump light; the second coupling assembly is configured to combine and interfere the first pump light and the second pump light to form a modulated pump light.

Optionally, the light emitting assembly includes: two lasers, one of which is used for generating the pumping light and the other is used for generating the detecting light; or alternatively

The light emitting assembly includes: the laser device comprises a laser device and a first beam splitter, wherein the laser device is used for generating a pulse beam, and the first beam splitter is used for dividing the pulse beam into the pumping light and the detection light and outputting the pumping light and the detection light.

Optionally, the interferometer modulator is specifically the optical fiber interferometer modulator, and the laser in the light emitting component is specifically an optical fiber laser; the light emitting assembly comprises a first beam splitter, and the first beam splitter is specifically an optical fiber beam splitter;

the fiber optic interferometric modulator further comprises: an optical fiber; the phase difference adjusting assembly comprises an optical fiber adjuster;

the first coupling assembly includes: the first port, the second port, the third port and the fourth port are respectively connected with the optical fibers; the other end of the first optical fiber connected with the first port is provided with the first reflecting mirror, and the other end of the second optical fiber connected with the second port is provided with the second reflecting mirror; the optical fiber adjuster is used for adjusting the length of the second optical fiber; the third port is used for receiving the pump light generated by the light emitting component; the fourth port is used for outputting the interference light generated by the first coupling component as the pump light after amplitude modulation.

Optionally, the first coupling component includes: a first optical fiber coupler; the first, second, third and fourth ports of the first fiber coupler serve as the first, second, third and fourth ports of the first coupling assembly.

Optionally, the first coupling component includes: a second fiber coupler and circulator connected by a fiber; the second optical fiber coupler comprises a first port, a second port, a third port and a fourth port; the circulator at least comprises a first interface, a second interface and a third interface; light input by the first interface can only exit from the second interface; light input by the second interface can only exit from the third interface; the second interface is connected with a third port of the second optical fiber coupler;

the first interface and the third interface are respectively used as a third port and a fourth port of the first coupling component; the first port and the second port of the second fiber coupler are respectively used as the first port and the second port of the first coupling component.

Optionally, the second optical fiber is coiled on the optical fiber regulator; the optical fiber adjuster is configured to change a length of the second optical fiber by an electrostrictive effect to change a phase of light transmitted in the second optical fiber.

Optionally, the interferometric modulator is in particular the non-fiber interferometric modulator, the position of the first mirror and/or the second mirror being adjustable; the first coupling component is a beam-splitting prism.

Optionally, when the time delay device is specifically the non-optical fiber type time delay device, the non-optical fiber type time delay device includes: a linear stage and a reflective assembly;

The linear platform carries the reflecting component and drives the reflecting component to move along a first direction or a second direction, and the first direction is opposite to the second direction;

when the reflecting component moves along the first direction, the time delay of the detection light relative to the pump light is linearly reduced; when the reflection assembly moves along the second direction, the time delay of the detection light relative to the pump light increases linearly.

Optionally, the measurement system further comprises: a time difference system; the time difference system is arranged on the transmission optical path of the pump light;

The time difference system is used for performing time difference processing on the pump light to obtain two pump light pulse sequences with fixed time delay, and synthesizing the two pump light pulse sequences with fixed time delay to obtain synthesized pump light.

Optionally, the phase difference adjusting component is configured to return two pump light pulses formed by splitting the same pump light pulse to the interference component by zero or an integer multiple of a repetition time period of the pump light pulses.

Optionally, the measurement system further comprises: a signal generator and a driver; the signal generator is used for sending a first signal with preset frequency to the driver; the driver is used for sending a driving signal with the preset frequency to the optical fiber regulator according to the first signal;

the optical fiber regulator is specifically configured to modulate the phase of the light transmitted in the second optical fiber at the preset frequency according to the driving signal.

Optionally, the measurement system further comprises: a lock-in amplifier and a signal processor;

the signal generator is further configured to send a second signal of the preset frequency to the lock-in amplifier;

the lock-in amplifier is used for demodulating the signal detected by the detector at the preset frequency according to the second signal and outputting the signal to the signal processor;

The signal processor is used for obtaining the detection information according to the signal demodulated by the phase-locked amplifier; the signal processor is further used for acquiring a relation curve between the time delay and the detection information according to the detection information when the detection light and the pump light have different time delays, and carrying out peak searching on the relation curve to obtain echo time; and calculating the thickness of the object to be detected according to the sound velocity in the object to be detected and the echo time.

In a third aspect, the present application provides a measurement method, wherein the measurement system provided in the second aspect is applied, and the method includes:

Generating pump light and probe light by using the light emitting assembly; the pump light is pulse light;

Amplitude modulating the pump light with the interferometric modulator; the interferometric modulator includes: an interference assembly and a phase difference adjustment assembly; the interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light;

Receiving the pump light or the probe light by using the time delayer, and adjusting delay time between the pump light pulse and the probe light pulse; the detection light and the pump light emitted by the time delay device are incident to an object to be detected; or the pump light and the detection light emitted by the time delay device are incident to the object to be detected; the pump light is used for forming sound waves in the object to be detected;

and acquiring signal light formed by reflecting the detection light by the object to be detected under a plurality of different delay times by using the detector, and acquiring detection information according to the signal light.

Optionally, the amplitude modulation of the pump light by the interferometer modulator specifically includes:

And utilizing the phase difference adjusting component to enable the time difference of returning the two pump light pulses formed by splitting the same pump light pulse to the interference component to be zero or integer times of the repetition time period of the pump light pulse.

Optionally, the interferometer modulator is specifically the fiber optic interferometer modulator, and the phase difference adjusting component includes: an optical fiber adjuster;

The method for performing amplitude modulation on the pump light by using the interferometer modulator specifically comprises the following steps:

the length of a second optical fiber in the fiber optic interferometric modulator is changed by the fiber optic adjuster to change the phase of light transmitted in the second optical fiber to cause interference in the interference assembly.

Compared with the prior art, the application has the following beneficial effects:

The measurement system provided by the application comprises a light emitting component, an interferometric modulator, a time delay and a detector. The light emitting component is used for generating pump light and detection light; the interferometer modulator is arranged on the transmission optical path of the pump light and is used for carrying out amplitude modulation on the pump light; the time delay device is used for receiving the pumping light or the detection light, so that the delay time between the pumping light pulse and the detection light pulse is adjustable; the detection light and the pump light emitted by the time delay device are incident to the object to be detected; or the pump light and the detection light emitted by the time delay device are incident to the object to be detected; the pump light is used for forming sound waves in the object to be detected; the detector is used for collecting signal light formed by reflection of detection light by the object to be detected in the scanning process of the delay time and obtaining detection information representing the light intensity of the signal light. Since the cost of the interferometric modulator is much lower than that of the acousto-optic modulator and the electro-optic modulator, the use of the interferometric modulator to amplitude modulate the pump light in the measurement system can save costs. Meanwhile, compared with an acousto-optic modulator and an electro-optic modulator, the interferometer modulator has stronger stability and ensures higher light utilization rate.

Drawings

In order to more clearly illustrate the embodiments of the application or the technical solutions of the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the application, and that other drawings can be obtained according to these drawings without inventive faculty for a person skilled in the art.

FIG. 1 is a schematic diagram of a measurement system according to an embodiment of the present application;

fig. 2 is a schematic structural diagram of a light emitting component according to an embodiment of the present application;

fig. 3 is a schematic structural diagram of a light emitting component according to an embodiment of the present application;

FIG. 4 is a schematic diagram of another measurement system according to an embodiment of the present application;

FIG. 5 is a schematic diagram of an interference assembly according to an embodiment of the present application;

FIG. 6 is a schematic diagram of a fiber optic interferometric modulator according to an embodiment of the application;

FIG. 7 is a schematic diagram of a first coupling assembly in a fiber optic interferometric modulator according to an embodiment of the application;

FIG. 8 is a schematic diagram of a non-fiber interferometric modulator according to an embodiment of the application;

FIG. 9 is a schematic diagram of an implementation of a reflective assembly according to an embodiment of the present application;

FIG. 10 is a schematic diagram of another implementation of a reflective assembly according to an embodiment of the present application;

FIG. 11 is a schematic diagram of an implementation of a further reflective assembly according to an embodiment of the present application;

Fig. 12 is a schematic structural diagram of an optical fiber type time difference system according to an embodiment of the present application;

FIG. 13 is a schematic diagram of a measurement system according to an embodiment of the present application;

fig. 14 is a flowchart of a measurement method according to an embodiment of the present application.

Detailed Description

In order to make the present application better understood by those skilled in the art, the following description will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the accompanying drawings, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

Fig. 1 is a schematic structural diagram of a measurement system according to an embodiment of the present application. As shown in fig. 1, a measurement system provided in an embodiment of the present application includes: a light emitting assembly 100, an interferometric modulator 200, a time delay 300, and a detector 400. The connection and function of each device in the measurement system will be described below.

The light emitting assembly 100 is used to generate pump light and probe light. In one possible implementation, the light emitting assembly 100 includes two lasers, laser 101A and laser 101B, respectively, as shown in fig. 2. Wherein the laser 101A is used to generate pump light and the laser 101B is used to generate probe light. In another possible implementation, the light emitting assembly 100 includes a laser 101C and a beam splitter 102 (hereinafter referred to as a first beam splitter), as shown in FIG. 3. The laser 101C generates a pulse beam, and the first beam splitter 102 splits the pulse beam into two beams, one beam being pumping light and the other beam being probe light. The pulse beams generated by the lasers 101A-101C described above may be ultra-short pulse beams, for example, having pulse widths of less than or equal to 1ps (picoseconds).

The pump light and the probe light are finally incident to the same incidence position of the object to be detected. The pump light is used for forming sound waves in the object to be detected and exciting ultrasonic signals. Thus, the reflectivity of the corresponding position of the object is changed. The photoacoustic measurement uses the change of the reflectivity of the object to be measured by the pump light.

The interferometer modulator 200 is disposed on a transmission optical path of the pump light outputted from the light emitting module 100, and is used for amplitude modulating the pump light. That is, the pump light is amplitude modulated by the interferometric modulator 200 before being incident on the object. By amplitude modulation, an enhancement of the pump light signal is achieved.

The interferometric modulator 200 includes an interferometric component and a phase difference adjustment component. The interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the first pump light and the second pump light are both pulse light. The phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light.

In this embodiment, the probe light is pulsed light. In other embodiments, the probe light is continuous light.

In a possible implementation, the phase difference adjusting component is specifically configured to return the two pump light pulses (i.e. the first pump light and the second pump light) formed by splitting the same pump light pulse to the interference component with a time difference of zero or an integer multiple of the repetition time period of the pump light pulses (specifically, the pump light pulses before being split into the two pump light pulses). For example, the repetition time period of the pump light pulse generated by the light emitting device 100 is T, i.e., one pump light pulse is transmitted every T times. The phase difference adjusting element is configured to cause the time difference between the first pump light and the second pump light returned to the interference element to be k×t, k being an integer.

The time delay 300 may be provided on the transmission path of the pump light as shown in fig. 1 or on the transmission path of the probe light as shown in fig. 4. Fig. 4 is a schematic structural diagram of another measurement system according to an embodiment of the present application. It can be understood that there is no time delay between the pump light and the probe light output from the light emitting assembly 100. When photoacoustic measurement (for example, film thickness measurement) is performed on an object to be measured, in the embodiment of the present application, there is a time delay between the pump light and the probe light incident on the object to be measured, and the time delay is adjustable. For this, the above-described time delay 300 is provided. In addition to the pump light path shown in FIG. 1, the pump light may also pass through the time delay 300 before passing through the interferometric modulator 200. The order of the interferometric modulator 200 and the time delay 300 is not limited herein. Referring to fig. 1 and 4, in an embodiment of the present application, the time delay 300 only needs to adjust the time delay of one light path.

The detector 400 may in particular be a photodetector for converting an optical signal into an electrical signal. In the technical scheme of the embodiment of the application, the detector 400 acquires signal light formed by reflecting the detection light by the object to be detected under a plurality of different delay times, and obtains detection information according to the signal light in the form of an electric signal through photoelectric conversion processing of the signal light. Specifically, the detection information may be obtained according to the light intensity information of the signal light, or may be detected according to the polarization information of the signal light and the position of the light spot. Scanning is specifically achieved by the time delay 300: the time delayer 300 continuously adjusts the delay time between the pump light and the probe light during the scanning of the delay time between the pump light and the probe light. The time delay 300 may specifically implement scanning of the delay time according to the electric driving signal.

Since the time delay 300 continuously adjusts the delay time between the pump light and the probe light during operation of the measurement system, the probe information obtained during the continuous acquisition and detection of the probe 400 also varies with the time delay. In this way, corresponding measurement results can be obtained according to this variation. For example, the thickness, sound velocity, young's modulus, and the like of the object to be measured are obtained.

The specific content of performing photoacoustic measurement on the object to be measured is not limited here. The implementation process of obtaining the probe information and obtaining the measurement result is not limited. The object to be measured may be a metal film, a dielectric film, etc., and the specific type of the object to be measured is not limited in this embodiment.

The above is the measurement system provided by the embodiment of the application. Since the cost of the interferometric modulator is much lower than that of the acousto-optic modulator and the electro-optic modulator, the use of the interferometric modulator to amplitude modulate the pump light in the measurement system can save costs. In the embodiment of the application, the periodically-changing modulation of the pump light signal is realized through the interferometer modulator, so that the subsequent signal extraction is facilitated. Meanwhile, compared with an acousto-optic modulator and an electro-optic modulator, the interferometer modulator has stronger stability and ensures higher light utilization rate.

The structure of the interference components in the measurement system is described below.

Fig. 5 is a schematic structural diagram of an interference component according to an embodiment of the present application. As shown in fig. 5, the interference assembly includes: a first coupling assembly 201, a first mirror M1 and a second mirror M2. The first coupling component 201 includes a plurality of ports, a first port P1, a second port P2, a third port P3, and a fourth port P4. The first port P1 corresponds to the first mirror M1, the second port P2 corresponds to the second mirror M2, and the third port P3 is configured to receive the pump light.

The pump light entering from the third port P3 is split into two beams at the first coupling assembly 201, and the two beams respectively exit from the first port P1 and the second port P2, reach the corresponding mirrors M1 and M2, are reflected back by the original paths at the mirrors M1 and M2, enter the first coupling assembly 201 from the first port P1 and the second port P2, and interfere at the first coupling assembly 201. The interference phenomenon modulates the amplitude of the pump light. The interference light exits from the fourth port P4 of the first coupling element 201 as amplitude modulated pump light.

The interferometer modulator 200 in the measurement system provided in the embodiment of the present application may be an optical fiber interferometer modulator or a non-optical fiber interferometer modulator. Interferometric modulators of different implementations are described and illustrated below in conjunction with the figures.

FIG. 6 is a schematic diagram of an optical fiber interferometer modulator according to an embodiment of the present application. As shown in fig. 6, the fiber optic interferometric modulator includes: an interference assembly (including a first coupling assembly 201, a first mirror M1, a second mirror M2), a phase difference adjustment assembly (including a fiber adjuster 202), and an optical fiber.

The four ports P1-P4 of the first coupling component 201 are each connected to an optical fiber. For convenience of the following description, the optical fiber connected to the first port P1 is referred to as a first optical fiber F1, and the optical fiber connected to the second port P2 is referred to as a second optical fiber F2. As shown in fig. 6, a first mirror M1 is provided at the other end of the first optical fiber F1, and a second mirror M2 is provided at the other end of the second optical fiber F2. The optical fiber and the reflecting mirror may be combined by two separate elements, or may be integrated when shipped from the factory. For example, the first mirror M1 is a reflector fixedly mounted on the end of the first optical fiber F1, and the second mirror M2 is a reflector fixedly mounted on the end of the second optical fiber F2.

In the fiber interferometer modulator, the fiber regulator 202 is provided with either one of the first optical fiber F1 and the second optical fiber F2. In fig. 6, the fiber regulator 202 is specifically configured with the second optical fiber F2. At this time, the optical fiber adjuster 202 is used to adjust the length of the second optical fiber F2. It should be noted that, when the optical fiber adjuster 202 adjusts the length of the second optical fiber F2, the phase of the light transmitted in the second optical fiber F2 is affected, so that the interference phenomenon of the light returned by the first optical fiber F1 and the second optical fiber F2 at the first coupling assembly 201 is interfered, and the modulation of the pump light amplitude is achieved.

In one possible implementation, the second optical fiber F2 may be coiled around the fiber adjuster 202. The optical fiber adjuster 202 may specifically be an optical fiber stretcher (PZT Fiber Stretcher) for changing the length of the second optical fiber F2 by the electrostrictive effect to change the phase of the light transmitted in the second optical fiber F2. The change of the length of the optical fiber by the electrostriction effect is a common function of the optical fiber stretcher, so the principle of the device in the embodiment of the application is not repeated.

In the fiber optic interferometric modulator implementation of FIG. 6, the lasers of the light emitting assembly 100 in the measurement system may specifically be fiber lasers in order to match the fiber optic interferometric modulator to increase the fiber optic path duty cycle in the overall measurement system. In addition, if the light emitting assembly 100 is configured as shown in FIG. 3 to include a laser and a first beam splitter, the first beam splitter may also be a fiber optic beam splitter. In this manner, the fiber laser is connected to the fiber optic splitter by the optical fiber, and the fiber optic splitter is also connected to the third port P3 of the first coupling assembly of the fiber optic interferometric modulator by the optical fiber.

In one possible implementation, the first coupling component 201 of the fiber optic interferometric modulator shown in FIG. 6 comprises a first fiber coupler. The four ports of the first fiber coupler are respectively four ports of the first coupling assembly 201. As an example, the split ratio of the first fiber coupler is 50:50. In this way, the pump light entering through the third port P3 is uniformly emitted from the first port P1 and the second port P2. Also, when the light returned from the first port P1 and the second port P2 interfere at the first optical fiber coupler, the interference light is also uniformly distributed to the third port P3 and the fourth port P4. The light emitted from the fourth port P4 may be directly used as the pump light after the amplitude modulation.

In another possible implementation, the first coupling component 201 of the fiber optic interferometric modulator may comprise: a second fiber coupler 2011 and a circulator 2012, as shown in fig. 7. The second fiber coupler 2011 includes a first port, a second port, a third port, and a fourth port; the circulator 2012 includes at least a first interface ①, a second interface ②, and a third interface ③.

As shown in fig. 7, light input by the first interface ① of the circulator 2012 can only exit from the second interface ② thereof; the light input by the second interface ② can only exit from its third interface ③. The second interface ② of the circulator 2012 is connected to a port of the second fiber coupler 2011, which port is referred to herein as a third port of the second fiber coupler 2011. The first port and the second port of the second optical fiber coupler 2011 are respectively used as the first port P1 and the second port P2 of the first coupling component 201. Since the second interface ② is capable of receiving the light incoming from the first interface ① and providing the light to the second optical fiber coupler 2011, the first interface ① is referred to as the third port P3 of the first coupling assembly 2011. The third interface ③ is capable of receiving the interference light transmitted by the second interface ②, and thus the third interface ③ is used as the fourth port P4 of the first coupling assembly 201.

The flow direction of the pump light propagating inside the fiber interferometric modulator is described below in connection with the fiber interferometric modulator structure shown in FIG. 6 and the first coupling assembly 201 structure shown in FIG. 7.

First, the pump light enters from the third port P3 of the first coupling assembly 201, i.e. into the first interface ① of the circulator 2012. And then transmitted to the second interface ②, enter the second optical fiber coupler 2011, exit from the first port P1 and the second port P2 of the second optical fiber coupler 2011, and reach the two mirrors M1 and M2 along the first optical fiber F1 and the second optical fiber F2, respectively. The two paths of light are reflected by the reflectors M1 and M2 respectively, then continue to return along the first optical fiber F1 and the second optical fiber F2, enter the second optical fiber coupler 2011 again from the first port P1 and the second port P2, meet inside the second optical fiber coupler 2011, and generate an interference phenomenon. The interference light is output from the other two ports of the second fiber coupler 2011 (one of which is fiber-coupled with the second interface ② of the circulator 2012). The light received by the second interface ② is transmitted out to the third interface ③ of the circulator (i.e., the fourth port P4 of the first coupling component 201).

As an example, the split ratio of the second optical fiber coupler 2012 is 50:50. In a possible implementation, the first and second optical fiber couplers 2012 are made by a fusion process.

In this embodiment, the pump light is linearly polarized light; the detection light is linearly polarized light. In other embodiments, the pump light is unpolarized light, circularly polarized light, or elliptically polarized light; the detection light is unpolarized light, circularly polarized light or elliptically polarized light.

The fiber optic interferometric modulator is described above in connection with fig. 6 and 7. Inside the fiber interferometer modulator, the optical path is a fiber optical path. A non-fiber interferometric modulator is described below in conjunction with fig. 8. FIG. 8 is a schematic diagram of a non-fiber interferometric modulator according to an embodiment of the application. In the non-fiber interferometric modulator of FIG. 8, the position of the first mirror M1 and/or the second mirror M2 is adjustable. As shown in fig. 8, the position of the second mirror M2 can be adjusted up and down, so as to change the transmission behavior of the light in the optical path corresponding to the second mirror M2, and implement the interference modulation of the interference phenomenon of the first coupling component 201. In a non-fiber interferometric modulator, the first coupling component 201 may be specifically a beam splitting prism. The phase difference adjusting component can be a motion mechanism for adjusting the position of the first reflecting mirror M1 and/or the second reflecting mirror M2, such as a manual or electric adjusting component, comprising a sliding rail and a motor; or a slide rail and a manual drive, etc. In one embodiment, the pump light is polarized light, such as linearly polarized light or elliptically polarized light; the beam splitting prism is a polarization beam splitter; in other embodiments, the pump light is unpolarized light.

An interference assembly comprising a first coupling assembly 201, a first mirror M1 and a second mirror M2 is described above in connection with fig. 5.

In another possible implementation, the interference assembly includes: the beam splitting assembly is used for splitting the pump light, and enabling the split pump light to generate the phase difference to form first pump light and second pump light. The first pump light and the second pump light directly enter the second coupling assembly. The second coupling assembly is configured to combine and interfere the first pump light and the second pump light to form a modulated pump light. The second coupling component specifically may include an optical fiber coupler, a fifth optical fiber and a sixth optical fiber connected to the optical fiber coupler; the phase difference adjusting assembly includes an optical fiber adjuster for adjusting a length of the fifth optical fiber and/or the sixth optical fiber, the optical fiber adjuster for changing the length of the fifth optical fiber and/or the sixth optical fiber by an electrostrictive effect.

The interferometer modulator provided by the embodiment of the application can overcome the defect of instability of an acousto-optic modulator and an electro-optic modulator, and has higher light energy utilization rate. The method is suitable for realizing amplitude modulation of the pump light in more complex or changeable scenes. In addition, the cost of the interferometer modulator is lower, so that the popularization and application of the technology are facilitated.

The implementation of other devices in the measurement system is described and illustrated below.

In the measurement system shown in fig. 1 and 4, the time delay 300 may be a fiber-optic type time delay or a non-fiber-optic type time delay. For the optical fiber type time delay, the input and output of light thereon are realized by an optical fiber, that is, the optical path from the light emitting assembly 100 to the time delay 300 in the measurement system shown in fig. 4 is an optical fiber optical path. If the interferometric modulator 200 employed in the measurement system of FIG. 1 is embodied as a fiber optic interferometric modulator and the time delay 300 is embodied as a fiber optic time delay, then the optical path from the interferometric modulator 200 to the time delay 300 is a fiber optic path. For a non-fiber time delay, it can be seen that both the input and output of light thereto are achieved through a spatial light path. Several implementations of the non-fiber time delay are described below.

In an embodiment of the present application, a non-optical fiber type time delay device includes: a linear stage and a reflective assembly. Wherein, the linear platform bears the reflecting component, can drive the reflecting component that it bears to move linearly: either linearly along a first direction or in a second direction opposite to the first direction. There are various implementations of the linear stage, for example, the linear stage may be movable as a whole, or the linear stage may include a linearly movable rail, and the reflective element is located on the rail and moves along with the rail.

When the reflecting component moves along the first direction, the time delay of the detection light relative to the pump light is linearly reduced; when the reflection assembly moves along the second direction, the time delay of the probe light relative to the pump light increases linearly.

The reflective component comprises a number of possible implementations. Fig. 9, 10 and 11 are schematic diagrams of three different implementations of the reflective assembly, respectively.

As shown in fig. 9, the reflection assembly includes a first reflection surface R1 and a second reflection surface R2, and a non-zero included angle is formed between the first reflection surface R1 and the second reflection surface R2. The probe light or the pump light enters the first reflection surface R1, is reflected by the first reflection surface R1, reaches the second reflection surface R2, and exits through the second reflection surface R2. The magnitude of the incidence angle of the pump light or the probe light incident on the first reflection surface R1 is not limited. In this implementation, the light incident to the reflecting element and the light exiting from the reflecting element are parallel to each other and located on the same side of the reflecting element, so that the adjustment of the delay time is facilitated when moving linearly.

In addition, the non-fiber time delay may also include two reflective components. In fig. 10, the non-optical fiber time delay device includes two opposite reflection assemblies, namely a first reflection assembly K1 and a second reflection assembly K2. Wherein the first reflecting component K1 is fixed, and the second reflecting component K2 is movable under the driving of a linear platform (not shown in fig. 10). The first reflecting assembly K1 and the second reflecting assembly K2 shown in fig. 10 each include two reflecting surfaces R1 and R2. In fig. 10, the pump light or the probe light enters from the first reflecting component K1 and finally exits from the second reflecting component K2. In practical applications, the pump light or the probe light may be first incident on the second reflecting component K2, and then the first reflecting component K1 emits the light beam (i.e. along the opposite direction of the arrow shown in fig. 10).

In the practice of the present application, there is no limitation on the number of reflective elements included in the non-fiber time delay. One, two or even more than two reflective elements may be included. Referring to fig. 11, the figure illustrates the structure of a non-fiber time delay containing four components. The non-fiber time delay of fig. 11 requires at least one reflective element to be stationary and at least one reflective element to move with the linear stage.

In the non-optical fiber type time delay device shown in fig. 10 and 11, when the linear stage moves by a distance Δx, the optical path difference between the probe light and the pump light changes by 2×Δx.

The above-mentioned interferometric modulator may be specifically a fiber optic interferometric modulator comprising a fiber optic adjuster as shown in fig. 6. Further, the measurement system provided by the embodiment of the application may further include: a signal generator and a driver. The signal generator is used for sending a first signal with preset frequency to the driver; the driver is used for sending a driving signal with the preset frequency to the optical fiber regulator according to the first signal; the optical fiber regulator is specifically configured to modulate the phase of the light transmitted in the second optical fiber at the preset frequency according to the driving signal.

The modulation at the preset frequency may be demodulated at the preset frequency. Thus, effective extraction of signals is achieved. The measurement system may further include: a lock-in amplifier and a signal processor; the signal generator is further configured to send a second signal of the preset frequency to the lock-in amplifier; the lock-in amplifier is used for demodulating the signal detected by the detector at the preset frequency according to the second signal and outputting the signal to the signal processor; the signal processor is used for obtaining the detection information according to the signal demodulated by the phase-locked amplifier.

In the foregoing, the measurement system provided by the embodiment of the application applies the photoacoustic measurement technology, and the pumping light excites the ultrasonic wave on the object to be measured and affects the reflectivity in the material. The signal light reflected by the object to be detected to the detector reflects the light intensity when the reflectivity changes along with the time delay of the pump light and the detection light. And thus can be used to peak and obtain measurements.

Assuming that the purpose of photoacoustic measurement is to measure the thickness of an object to be measured, in the embodiment of the present application, the signal processor may obtain a relationship curve between time delay and probe information according to the probe information when the probe light and the pump light have different time delays, and peak-finding the relationship curve to obtain the echo time t _echo. And the signal processor calculates the thickness d of the object to be detected according to the sound velocity v _s in the object to be detected and the echo time t _echo. The calculation formula of the thickness of the object to be measured is as follows:

d=v _s*t_echo/2 formula (1)

In the above-described relationship, the initial time is a time when the optical path difference between the pump light and the pulse light is 0. The echo time is a time corresponding to a first peak after the initial time except noise when the peak is found. The echo time t _echo can be obtained by making a difference between the echo time and the initial time.

In the measurement system provided by the embodiment of the application, in order to eliminate the background signal and the low-frequency component in the signal, reduce noise and improve the sensitivity of measurement, the measurement system can further comprise a time difference system. The time difference system is also beneficial to extracting effective detection information from the signal light. The time difference system is specifically arranged on the transmission optical path of the pump light. The time difference system is used for performing time difference processing on the pump light to obtain two pump light pulse sequences with fixed time delay, and synthesizing the two pump light pulse sequences with fixed time delay to obtain synthesized pump light. As an example, the fixed delay Δt takes a value between 0.1ps and 10 ps.

In the embodiment of the application, the time difference system can be an optical fiber type time difference system or a non-optical fiber type time difference system. The former is an optical fiber path inside, and the latter is a spatial path inside. An implementation of the fiber-optic time-difference system is described below.

Fig. 12 is a schematic structural diagram of an optical fiber type time difference system according to an embodiment of the present application. The optical fiber type time difference system 600 includes: a second fiber splitter 601, a third fiber F3, a fourth fiber F4, and a fiber coupler 604. Wherein, the third optical fiber F3 and the fourth optical fiber F4 are connected with the second optical fiber beam splitter 601 at one end and the optical fiber coupler 604 at the other end.

In the optical fiber time difference system 60, the lengths of the third optical fiber F3 and the fourth optical fiber F4 are different, so that the two pump light paths in the third optical fiber F3 and the fourth optical fiber F4 keep a fixed delay.

The second optical fiber splitter 601 is configured to split the pump light incident on the optical fiber type time difference system 60 into a first light beam and a second light beam, where the first light beam is transmitted to the optical fiber coupler 604 through the third optical fiber F3, and the second light beam is transmitted to the optical fiber coupler 604 through the fourth optical fiber F4. The optical fiber coupler 604 couples the two received light beams with a fixed delay through the third optical fiber F3 and the fourth optical fiber F4, and outputs the combined pump light (combined into a pulse sequence).

Let the difference in length of the third optical fiber F3 and the fourth optical fiber F4 be Δl, where Δl can be adjusted, i.e. to a desired value, as desired. And if the light velocity in the fiber core is v, the calculation formula of the fixed delay delta t of the synthesized pump light is as follows:

Δt=Δl/v equation (2)

In the measurement system provided by the embodiment of the application, by arranging the time difference system, the background signal and the low-frequency component in the signal are eliminated, the noise signal is reduced, and the convenience and the accuracy of signal extraction are correspondingly improved, so that the weak signal can be detected, and the measurement sensitivity is improved. For an analyte comprising multiple stacked thin films, the technique improves the measured signal-to-noise ratio for each layer thickness, improving the selectivity to thin layers buried under thicker layers, allowing weak signals to be detected.

Fig. 13 is a schematic structural diagram of yet another measurement system according to an embodiment of the present application. As shown in fig. 13, the measurement system includes: light emitting assembly 100, fiber optic interferometric modulator 200, non-fiber optic time delay 300, detector 400, driver 500, signal generator 700, lock-in amplifier 800, and signal processor 900.

In the measurement system shown in fig. 13, since the non-optical fiber type time delay 300 is used, the optical path inside the delay 300 is a spatial optical path. The non-optical fiber type time delay 300 is disposed on the transmission optical path of the probe light, and it is understood that it may also be disposed on the transmission optical path of the pump light. A first fiber collimator C1 is also included in the system.

The first fiber collimator C1 is configured to provide the parallel detection light generated by the light emitting assembly 100 to the non-fiber time delay 300. If the non-optical fiber type time delay 300 is specifically disposed on the transmission optical path of the pump light, the first optical fiber collimator C1 is also disposed on the transmission optical path of the pump light, and is used to provide the pump light generated by the light emitting assembly 100 to the non-optical fiber type time delay 300 in parallel.

The conversion from the optical fiber path to the spatial path is achieved by the first fiber collimator C1. Further, as shown in fig. 13, a lens or a lens group L0 may be provided between the first fiber collimator C1 and the non-fiber type time delay 300, and the lens or the lens group L0 may be used for beam expansion, spot size adjustment, or the like.

As shown in fig. 13, the measurement system may further include: a second fiber collimator C2, a third fiber collimator C3 and a first group lens L1 between the non-fiber type time delay 300 and the object to be measured. Wherein the second optical fiber collimator C2 and the third optical fiber collimator C3 are connected through optical fibers. As shown in fig. 13, the probe light (or pump light) emitted from the time delay 300 enters the optical fiber through the second optical fiber collimator C2, and is transmitted to the third optical fiber collimator C3 by the optical fiber. The third fiber collimator C3 is for collimating the probe light transmitted by the connected optical fibers into parallel light. The first group lens L1 may include at least one lens for converging the parallel light emitted from the third fiber collimator C3 onto the surface of the object to be measured.

Further alternatively, as shown in fig. 13, a lens or lens group L0 may be provided between the third fiber collimator C3 and the first group lens L1 for beam expansion, convergence, spot size adjustment, and the like. Alternatively, a lens or lens group L0 may be provided between the non-optical fiber type time delay 300 and the second optical fiber collimator C2 for beam expansion, convergence, spot size adjustment, etc. The second fiber collimator C2 realizes the conversion from the spatial light path to the fiber light path. The third fiber collimator C3 realizes the conversion from the fiber light path to the space light path.

As shown in fig. 13, the measurement system may further include: a fourth fiber collimator C4 and a second group lens L2 on the transmission optical path of the pump light. The fourth fiber collimator C4 is configured to collimate the synthesized pump light output by the time difference system 600 into parallel light, and the second lens group L2 is configured to converge the parallel light emitted from the fourth fiber collimator C4 onto the surface of the object to be measured. Wherein the second group of lenses L2 may comprise at least one lens. Optionally, a lens or lens group L0 may also be provided between the fourth fiber collimator C4 and the second group lens L2 for beam expansion, focusing, spot size adjustment, etc.

As can be seen from fig. 13 and the measurement system described above, the pump light path is a complete fiber structure path. When the time delay 300 is embodied as a fiber-optic type time delay, the probe light path may also realize a complete fiber-optic structure path. The fourth fiber collimator C4 realizes conversion from the fiber optical path to the spatial optical path.

The coverage of the optical fiber optical path in the measuring system avoids most of optical path adjustment work, the time consumption of the whole system construction process is shortened, and the efficiency is improved. In addition, the stability and anti-interference performance of the system are greatly improved. Can be suitable for more and more complex application scenes.

In other embodiments, if the light emitting assembly 100 includes one laser and one beam splitter, the beam splitter may be replaced with a polarizing beam splitter. For example, p light is split as pump light, s light as probe light; or s light is split to be used as pump light, and p light is used as detection light. The polarization directions of p light and s light are mutually perpendicular.

In the measurement system of the above embodiment, the probe light and the pump light are incident to the same point of the object to be measured, and in other embodiments, the probe light and the pump light are incident to different points of the object to be measured, so as to detect defects, elastic modulus, thickness, and the like in the portion of the object to be measured between the incidence positions of the probe light and the pump light.

Based on the measurement system provided by the foregoing embodiment, correspondingly, the application further provides a measurement method for realizing measurement by applying the system. The measuring method is described and illustrated below with reference to the accompanying drawings.

Fig. 14 is a flowchart of a measurement method according to an embodiment of the present application. As shown in fig. 14, the measurement method includes:

S1401: generating pump light and probe light by using the light emitting component; the pump light is pulse light;

S1402: amplitude modulating the pump light with an interferometric modulator; the interferometric modulator includes: an interference assembly and a phase difference adjustment assembly; the interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light;

S1403: receiving the pumping light or the detection light by using a time delay device, and adjusting the delay time between the pumping light pulse and the detection light pulse; the detection light and the pump light emitted by the time delay device are incident to the object to be detected; or the pump light and the detection light emitted by the time delay device are incident to the object to be detected; the pump light is used for forming sound waves in the object to be detected;

S1404: and acquiring signal light formed by reflecting the detection light by the object to be detected under a plurality of different delay times by using the detector, and acquiring detection information according to the characterization signal light.

Since the interferometer modulator is used to amplitude modulate the pump light in the measurement system implementing the measurement method shown in fig. 14, the cost of the interferometer modulator is far lower than that of the acousto-optic modulator and the electro-optic modulator, so that the use of the interferometer modulator to amplitude modulate the pump light in the measurement system can save the cost. Meanwhile, compared with an acousto-optic modulator and an electro-optic modulator, the interferometer modulator has strong stability and ensures high light utilization rate, so that the light energy utilization rate of photoacoustic measurement is high, and the measurement process and the measurement result are more stable.

Optionally, step S1402 may specifically include:

And utilizing the phase difference adjusting component to enable the time difference of two pump light pulses formed by splitting the same pump light pulse to return to the interference component to be zero or integer times of the repetition time period of the pump light pulse.

It can be seen that, in the embodiment of the present application, by performing step S1402, the periodically varying modulation of the pump light signal can be achieved, for example, to keep the time difference between the two pump light pulses in the interference component to be zero, or to reach the expected integer multiple of the repetition time period of the pump light pulses. The multiple may be set according to the actual amplitude modulation requirements. For example, take a multiple of 3.

If the interferometric modulator in the measurement system is specifically a fiber optic interferometric modulator (see the structure shown in FIG. 6), then step S1402 may specifically include:

The length of a second optical fiber in the optical fiber interferometric modulator is changed by the optical fiber adjuster to change the phase of light transmitted in the second optical fiber so that interference occurs in the interference assembly.

The modulation mode is very convenient, and only one optical fiber is required to be coiled on the optical fiber modulator.

In one possible implementation manner, in order to eliminate a background signal and a low-frequency component in a signal, reduce noise and improve measurement sensitivity, the measurement method provided by the embodiment of the application may further include:

And performing time difference processing on the pump light by using a time difference system to obtain two pump light pulse sequences with fixed time delay, and synthesizing the two pump light pulse sequences with fixed time delay to obtain synthesized pump light.

By the time difference processing of the time difference system, the background signal and the low-frequency component in the signal are eliminated, the noise signal is reduced, the convenience and the accuracy of signal extraction are correspondingly improved, and the measurement sensitivity is improved. At the same time, for an object to be measured comprising a plurality of stacked thin films, the technique improves the measured signal-to-noise ratio for each layer thickness, improving the selectivity to thin layers buried under thicker layers.

In one possible implementation, the measurement method may further include: acquiring a relation curve between the time delay and the detection information according to the detection information when the detection light and the pump light have different time delays by a signal processor, and carrying out peak searching on the relation curve to acquire echo time; and calculating the thickness of the object to be measured according to the sound velocity and the echo time in the object to be measured.

By executing the measuring method, the thickness of the object to be measured is accurately measured. In other scenarios, the detection information may be used to obtain surface flaw information (e.g., position, size) of the object to be measured, or to obtain a dimensional parameter of the object to be measured. The specific scene of performing photoacoustic measurement to the above-described measurement system and measurement method is not limited herein.

It should be noted that, in the present specification, each embodiment is described in a progressive manner, and identical and similar parts of each embodiment are all referred to each other, and each embodiment is mainly described in a different point from other embodiments. Those of ordinary skill in the art will understand and implement the present invention without undue burden.

The foregoing is only one specific embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions easily contemplated by those skilled in the art within the technical scope of the present application should be included in the scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A measurement system, comprising: a light emitting assembly, an interferometric modulator, a time delay, a detector, and a signal processor;

The interferometer modulator is arranged on the transmission optical path of the pump light and is used for carrying out amplitude modulation on the pump light; the interferometric modulator includes: an interference assembly and a phase difference adjustment assembly; the interference component is used for enabling the pump light to form first pump light and second pump light with phase differences and enabling the first pump light and the second pump light to interfere; the phase difference adjusting component is used for adjusting the phase difference between the first pump light and the second pump light so that the time difference between the first pump light and the second pump light returning to the interference component is zero or an integral multiple of the repetition time period of the pump light pulse;

The time delay device is used for receiving the pumping light or the detection light, so that the delay time between the pumping light pulse and the detection light pulse is adjustable; the detection light and the pump light emitted by the time delay device are incident to an object to be detected; or the pump light and the detection light emitted by the time delay device are incident to the object to be detected; the pump light is used for forming sound waves in the object to be detected so as to influence the reflectivity of the material of the object to be detected;

the detector is used for acquiring signal light formed by reflecting the detection light by the object to be detected under a plurality of different delay times and acquiring detection information according to the signal light; the signal light reflects the light intensity when the reflectivity changes along with the time delay of the pump light and the detection light;

The signal processor is used for acquiring a relation curve between time delay and detection information according to the detection information when the detection light and the pump light have different time delays, and carrying out peak searching on the relation curve to obtain echo time; and calculating the thickness of the object to be detected according to the sound velocity in the object to be detected and the echo time.

2. The measurement system of claim 1, wherein the interference assembly comprises: a first coupling assembly, a first mirror, and a second mirror;

3. The measurement system of claim 2, wherein the light emitting assembly comprises: two lasers, one of which is used for generating the pumping light and the other is used for generating the detecting light; or alternatively

4. A measurement system according to claim 3, wherein the interferometric modulator is in particular a fibre optic interferometric modulator, and the laser in the light emitting assembly is in particular a fibre optic laser; the light emitting assembly comprises a first beam splitter, and the first beam splitter is specifically an optical fiber beam splitter;

5. The measurement system of claim 4, wherein the first coupling assembly comprises: a first optical fiber coupler; the first, second, third and fourth ports of the first fiber coupler serve as the first, second, third and fourth ports of the first coupling assembly.

6. The measurement system of claim 4, wherein the first coupling assembly comprises: a second fiber coupler and circulator connected by a fiber; the second optical fiber coupler comprises a first port, a second port, a third port and a fourth port; the circulator at least comprises a first interface, a second interface and a third interface; light input by the first interface can only exit from the second interface; light input by the second interface can only exit from the third interface; the second interface is connected with a third port of the second optical fiber coupler;

7. The measurement system of any one of claims 4-6, wherein the second optical fiber is coiled on the fiber optic regulator; the optical fiber adjuster is configured to change a length of the second optical fiber by an electrostrictive effect to change a phase of light transmitted in the second optical fiber.

8. The measurement system according to claim 2, wherein the interferometric modulator is in particular a non-fiber interferometric modulator, the position of the first mirror and/or the second mirror being adjustable; the first coupling component is a beam-splitting prism.

9. The measurement system according to any one of claims 1-6, wherein when the time delay is in particular a non-fiber-optic time delay, the non-fiber-optic time delay comprises: a linear stage and a reflective assembly;

10. The measurement system of any one of claims 1-6, 8, further comprising: a time difference system; the time difference system is arranged on the transmission optical path of the pump light;

11. The measurement system of any of claims 4-6, further comprising: a signal generator and a driver; the signal generator is used for sending a first signal with preset frequency to the driver; the driver is used for sending a driving signal with the preset frequency to the optical fiber regulator according to the first signal;

12. The measurement system of claim 11, further comprising: a phase-locked amplifier;

The signal processor is further configured to obtain the detection information according to the signal demodulated by the lock-in amplifier.

13. A measurement method, characterized in that the measurement system according to any one of claims 1-12 is applied, the method comprising:

acquiring signal light formed by reflecting the detection light by an object to be detected under a plurality of different delay times by using the detector, and acquiring detection information according to the signal light;

Acquiring a relation curve between the time delay and the detection information according to the detection information when the detection light and the pump light have different time delays by a signal processor, and carrying out peak searching on the relation curve to acquire echo time; calculating the thickness of the object to be measured according to the sound velocity and the echo time in the object to be measured; the method for performing amplitude modulation on the pump light by using the interferometer modulator specifically comprises the following steps:

14. The method according to claim 13, wherein the interferometric modulator is in particular a fiber optic interferometric modulator, and the phase difference adjustment assembly comprises: an optical fiber adjuster;